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November 1998

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1998.11.12 15:54 "Re: Revison 7.0", by Tom Lane
1998.11.12 22:38 "Re: Revison 7.0", by Mark Knibbs
1998.11.13 15:59 "Re: Revison 7.0", by Tom Lane

1998.11.12 22:38 "Re: Revison 7.0", by Mark Knibbs

On 12-Nov-98, Dr. Klaus Bartz wrote:
> a 4 color image imported from HPGL/2. TIFF RAW 79 MB,
> TIFF deflate 950 KB, TIFF RAW and then bzip2 290 KB.
> Very special, yes. But is there not a market for colored technical
> prints in the future?

For applications like this, I think it would be useful to be able to use CCITT
group 4 compression.

For example, suppose you are digitising some documentation which only uses two
ink colours, black mainly and perhaps red for highlighted text. You could
digitise the black separately from the red, ending up with two G4-compressed
images for the same page.

Image viewers could either just show the black, or both colours. For monochrome
screens or printers, programs could logical-OR the pixels of both images
together.

Of course this same system would work for four-colour images. It could be
extended to any number of colours simply.

It would be nice if there were some way in the TIFF spec to describe that
multiple G4-compressed images are related in this way. For digitising
spot-colour documents G4 probably gives better compression than other methods.


This "multiple images for the same page" idea could be extended in a more
general way. When digitising a document which includes colour photographs as
well as normal black-on-white text, a G4-compressed image could hold all
except the photos (in the G4 image photo area would be replaced with white
background). An associated colour image, maybe using JPEG compression, would
also be present, which could be overlaid on the text by programs that support
this feature.


-- Mark